Garden Design Drainage
DRAINAGE. One of the greatest drawbacks to successful gardening is badly drained ground. Wherever water lies in the ground at a depth easily reached by the roots of most cultivated plants they do not thrive, except where the water is constantly on the move, such as the bank of a river, brook or lake; there many plants will flourish. There are some wild plants that succeed in soil that has reached a water logged state, but generally such land is useless for gardening, farming or forestry purposes unless steps are taken to free it from superfluous moisture.
Heavy clayey land or soil overlying a hard subsoil is very subject to water logging; so, too, is low-lying land which is little above the high water mark of a river or lake in the vicinity.
How Deep to Lay Drain tiles. When undertaking drainage operations, it is necessary, first, to find whether there is a natural fall from the land in question to a brook, river, lake or pond in the vicinity, and the gradient of the fall. As a rule, it is wise to lay one or more main drains with which side branch drains, laid in herringbone fashion, are connected at such intervals as are likely to carry off the superfluous moisture. The main drains will need to be about 21/2 or 3 ft. beneath the surface, with a slight fall to the outlet; the branch drains may start 15-18 in. deep and fall gradually.
For the main drains, agricultural drain tiles 6 in. in diameter with open joints will usually suffice, the side drains being of similar tiles 4 in. in diameter. The pipes should be laid on an even, gently sloping bottom and around them and over them a layer of loose rubble, gravel or cinders should be placed. In woodlands a series of open drains or ditches answers better than drain-tiles, but the ditches should be cleaned annually.
Flowerpots and pans and flats in which plants
are grown, as well as tubs and greenhouse benches, must always be adequately drained; if drainage is not assured, the soil soon becomes waterlogged and “sour” and the plants deteriorate.
These various containers for soil are furnished with holes or narrow slits in their bottoms to permit the escape of superfluous moisture. To facilitate this escape it is usual to place some “drainage material,” often referred to as simply “drainage,” in the bottoms of the containers before the soil is filled in. In the case of pots, pans and tubs, and often flats, this consists of a layer of crocks (pieces of broken flowerpot), coarse cinders or gravel, covered with some coarse organic material such as half-decayed leaves, straw manure or grass turf from which most of the soil has been shaken. Greenhouse benches and, often, flats are drained by placing in their bottoms a layer of coarse organic matter alone without any under layer of crocks, cinders or gravel.
Air drainage is an important matter to consider in gardening. Just as water flows down a slope, so does cold air, and being heavier than warm air, in hollows and valleys at the bottom of slopes it displaces the latter and accumulates. Thus it is that sites at the bottoms of slopes are likely to experience lower temperatures, and these will last for longer periods than they will in locations at somewhat higher elevations.
Because of this, low-lying sites should be avoided when setting out plants on the border line of tenderness and also when planting fruit trees and other early-flowering trees and shrubs that may have their flowers destroyed by a late spring frost. It is a common experience to have fruit blossoms damaged on low-lying sites when those of the same kinds of trees planted at higher elevations are spared.